This invention relates to flexible power transmission belts and the cushion stocks used therein. Any power transmission belt with a cushion stock will benefit by the practice of the present invention, whether it be a power drive belt, a V-belt, a multi-ribbed V-belt, or any other type of power transmission belt. Power transmission belts which will benefit by the practice of the present invention include, but are not limited to the belts described and illustrated in U.S. Pat. No. 2,057,852; 3,404,576; 3,404,577; 3,416,383; 3,643,518; 3,667,308; 3,951,006; 4,213,350; and 4,342,561. A belt which particularly benefits by the practice of the present invention is the multi-ribbed V-belt.
These well known belts are characterized by such basic elements as a tensile member composed of a rubber insulated cord layer and a cushion member. Often the belt is covered by a rubberized fabric envelope which covers the entire surface of the belt. As a result of the severe operating conditions to which belts are often subjected, the resistance of the belts to failure due to flexing has become increasingly important. Flexing is particularly severe with multi-ribbed transmission belts. In particular, the higher temperature environments, such as are found in the engine compartments of automobiles, have a detrimental effect on the useful life of a belt. It is, therefore, desirable to improve the durability of these belts, especially where higher operating temperatures are likely to be found.